In MIMO transmission between M transmission antennas and N reception antennas, a transmission signal vector is set as a vector having 2M elements comprising in-phase components and quadrature components of M complex signals, a reception signal vector is set as a vector having 2N elements comprising in-phase components and quadrature components of N complex signals, and a transfer matrix is set as a real matrix comprising 2N rows and 2M columns. Then, a transfer matrix containing IQ mismatch is obtained based on a training signal, thereby executing MIMO encoding and decoding. For learning of the transfer matrix, a training signal which has two linearly-independent signal points on a constellation for each of the transmission antennas is used. With such an arrangement, in MIMO transmission, IQ mismatch in a quadrature modulator and a quadrature demodulator can be compensated and a bit error rate can be improved.